Field of the Invention
The present invention relates to a laminated film, and more particularly, to a laminated film that is used in a packaging container so that the contents can be appropriately heated in a microwave oven and a packaging bag using a laminated film.
Description of Related Art
There are various foods that are contained in a packaging container, such as a packaging bag, in a cooked or semi-cooked state so as to be able to be stored at room temperature, or at a low temperature, or in a frozen state and that can be eaten by being heated in a microwave oven without being opened.
When the packaging container is heated in the microwave without being opened, moisture in the packaging container becomes water vapor. Accordingly, the volume of the packaging container is increased. For this reason, there is a risk of rupture or the like of the packaging container if there is no gap through which water vapor can be discharged. On the other hand, when the contents are in a semi-cooked state or the like, it may be necessary to not only simply heat the contents but also steam the contents with the generated water vapor. In this case, if a hole or the like for discharging vapor is excessively large, steaming is not sufficiently performed. Accordingly, there is a problem, such as a reduction in the taste.
Some packaging bags corresponding to the above applications are known. All of these packaging bags are generally formed using a laminated film. When internal pressure increases, a crack is generated in a part of the laminated film, and water vapor is discharged through the crack. Thus, rupture is prevented.
As a packaging bag in which the contents can be steamed during the heating by a microwave, for example, a packaging bag disclosed in PCT International Publication No. WO2012/086295 is known. In the packaging bag, a slit passing through an outer layer and an inner layer is formed in a part of a laminated film having the outer layer and the inner layer and then the inner layer is heated and melted so that only the slit of the inner layer is closed. When heating the packaging bag in the microwave, the inner layer tears and a small hole is formed. Therefore, since water vapor is not excessively discharged, it is possible to perform steaming while preventing rupture.
However, although it is possible to perform steaming while preventing rupture in the packaging bag disclosed in PCT International Publication No. WO2012/086295, processing on the formation and re-fusing of the slit is complicated. Therefore, the manufacturing process is complicated, and it is difficult to improve the manufacturing efficiency. In addition, it is difficult to guarantee the sealing quality after re-fusing.